(1) Field of the Invention
This invention relates to the beneficiation of phosphate ore by froth flotation using an anionic flotation agent comprised of naturally derived fatty acids and, as a promoter, a salt of an ether sulfate. More specifically, the fatty acids are derived from a vegetable or animal oil and the ether sulfate is of the general formula EQU R(OCH.sub.2 CH.sub.2).sub.n OSO.sub.3.sup.- M.sup.+
wherein M.sup.+ is selected from the group consisting of Na.sup.+, K.sup.+ and NH.sub.4.sup.+, n is from 1 to 6 and R is an alkylaryl group or CH.sub.3 (CH.sub.2).sub.x --wherein x is from 6 to 20.
(2) Description of the Prior Art
Agents, often called collectors, are used in conjunction with froth flotation to aid in the beneficiation of phosphate, P.sub.2 O.sub.5, from phosphate rock. Phosphate rock is a natural rock consisting largely of calcium phosphate and used chiefly as a raw material for manufacture of phosphate fertilizers, phosphoric acid and phosphorus, and therefore indirectly used for practically all commercial phosphorus chemicals. Important deposits of phosphate ore are in Florida, North Carolina, Tennessee, Wyoming, Montana, Utah, Idaho and North Africa. The deposits, however, also contain siliceous materials, such as silica which are valueless constituents. Other valueless constituents such as calcium carbonate, some carbonaceous materials and heavy minerals may also be present.
Many methods have been used to beneficiate or concentrate the phosphatic constituents by flotation from the siliceous, carbonaceous and heavy mineral constituents. Froth flotation is the principal means by which phosphate and other ores are concentrated.
Flotation, generally, is a process for separating finely ground valuable minerals from their associated gangue, or waste, or for separating valuable components one from another. In froth flotation frothing occurs by introducing air into a pulp of finely divided ore and water containing a frothing agent. Minerals that have a special affinity for air bubbles rise to the surface in the froth and are separated from those wetted by the water. The particles to be separated by froth flotation must be of a size that can be readily levitated by the air bubbles.
Froth flotation agents used in conjunction with flotation must be capable of selectively coating the desired material in spite of the presence of many other mineral species.
Commonly, partial concentration is first employed to remove slimes and the phosphate values are then extracted from the sized slurry using two froth flotation beneficiation separations.
The first involves a flotation of phosphate values through the use of an anionic flotation agent such as a fatty acid and caustic in combination with a petroleum fraction, such as kerosene. These reagents are mixed with the aqueous suspension of phosphate rock and the mixture is agitated and aerated or frothed. The phosphate values tend to concentrate in the upper portion of the cell for separation.
The enriched fraction, typically known as the rough concentrate, still contains 8% to 20% siliceous matter which is attempted to be separated from the phosphate rock in a second flotation using a cationic reagent. The cationic reagents used have been long chain fatty acid amines or the salts, thereof.
Various promoters for the anionic flotation of phosphate rock with fatty acids are known in the prior art. (A promoter is a substance which when added to the flotation reagent significantly increases the recovery and/or grade of the phosphate material thereby greatly increasing the efficiency and economics of the flotation process.) Generally speaking, the addition of surfactants to the flotation reagents leads to a trade off between these two parameters. Usually an increase in recovery leads to a corresponding drop in selectivity and vice versa. In today's market, recovery is of utmost importance and consequently promoters which address themselves primarily to increases in recovery are available.
U.S. Pat. No. 3,353,672 discloses as superior reagents for use as collectors for phosphate rock particles chlorinated saturated fatty acids having from 12 to 22 carbon atoms and a melting point between 0.degree. C. and 20.degree. C., preferably chlorinated palmitic acid containing approximately 25% chlorine by weight and chlorinated stearic acid containing approximately 48% chlorine by weight.
U.S. Pat. No. 3,361,257 discloses an improvement in beneficiation of phosphate ores by anionic froth flotation by the addition of from 0.1 to 2.5 pounds sodium fluoride per ton of ore feed, at pH 7.6-9.6, in the conditioning tanks prior to the addition of the anionic reagent.
U.S.S.R. Pat. No. 357,004 teaches the use of the alkali metal soaps of monobasic and dibasic carboxylic acids as the agglomerating agent to improve the flotation of phosphate ores.
In India, Atomic Energy Commission, Bhabha Atomic Research Center [Report] 1976, B.A.R.C.--857, discloses a phosphate flotation agent comprised of a mixture of linoleic acid, diesel oil and amyl alcohol.
In Neftepererab. Neftekhim. (Moscow) 1977, a flotation reagent for phosphorite ores is prepared by: oxidation of paraffins at from 165.degree. C. to 170.degree. C. in the presence of 4% boric acid to give a product with an acid number of 40 to 50; washing the product with hot water; saponifying with 40% sodium hydroxide solution at 170.degree. C. for 30 minutes; separating the soap; and diluting with water.
U.S. Pat. No. 4,138,350 describes a combination of a fatty acid and a monoester of sulfosuccinic acid or salt thereof for the improved recovery of non-sulfide ores by froth flotation.
U.S. Pat. No. 4,139,481 describes a combination of a fatty acid and an alkylamidoalkyl monoester of a sulfosuccinic acid or salt thereof as a non-sulfide ore recovery agent in the froth flotation process.
Finally, U.S. Pat. No. 4,139,482 discloses the combination of a fatty acid and an N-sulfodicarboxylic acid aspartate for boostering the recovery of non-sulfide minerals.
As earlier stated, the prior art addresses improving recovery which is only one of the two factors affecting the economics of phosphate flotation.